The present invention relates to a sensor for sensing water such as rain or dew on transparent plates such as windshields of vehicles, and window panes of houses or other facilities, to turn on wipers, defroster, warning device or some other device, and a system for producing holograms usable in such sensors.
Japanese Patent Provisional (Kokai) Publications Nos. H10(1998)-96791, H10(1998)-62336 and H9(1997)-257952 show rain or dew sensors having light emitting and light receiving elements.